Book excerpt: A high-resolution forward-scatter system can be effectively used to study the tropospheric refractive-index structure over extended volumes of space. This report is a theoretical analysis of the performance of scan experiments in which the common volume is systematically moved through space by swinging the narrowbeam transmitter and receiver antennas in azimuth and elevation. Experimental evidence points toward a layered composition of the tropospheric refractive index. Various models of single or multiple layers of turbulent refractive-index perturbations, including vertical-layer widths that are a fraction of the common volume lateral dimensions, are used to simulate tropospheric conditions and to compute the spatial response of a narrowbeam forward-scatter system. The rather complex forward-scatter geometry along the great circle path and at a horizontal distance from it is evaluated in enough detail to allow accurate determination of scatter signals. The effect of specular contributions is included to show how a reflection term typically superposes on the scatter signal when the refractive-index field is analyzed. Refractive-index structures are constantly being changed and new ones produced by such parameters as wind and turbulence. Hence, the information obtained from the high-resolution forward-scatter system also relates to these parameters. (Author).